Overview

Comprehensive Description

Scaridae: The Parrotfishes

Parrotfishes are abundant on coral reefs, where they often are the largest component of the fish biomass. They are generally small to medium-sized herbivorous fishes. Depth distribution is primarily 1-30m, with some species occurring down to 80m. Adult scarids are grazing animals, feeding on the close-cropped algal and bacterial mat covering dead corals and rocks, seagrasses, and by crushing bits of coral that may contain invertebrate prey. Juveniles feed on small invertebrates. Parrotfishes feed continuously during the day, often in mixed schools, biting at rocks and corals. They usually scrape some of the coral or ingest sand while feeding and grind this in their pharyngeal mill with the plant food. In pulverizing the coral rock fragments and sand they create substantial quantities of sediment. In many areas they are probably the principal producers of sand. Two types of spawning behaviour have been observed for some scarids. Spawning may take place in an aggregation of initial-phase fish; individual groups of fish dart upward from the aggregation, releasing eggs and sperm at the peak of these upward dashes. The second pattern of reproduction consists of pair-spawning; a terminal male defends a territory from other males, courts females within his territory, and spawns individually with them. At night, some species of Scarus are capable of secreting an enveloping cocoon of mucus in which the fish sleeps until daylight.

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Scarids, which are widely known as parrotfishes because of their beak-like jaws, include approximately nine genera and 83 species. They are abundant in tropical reefs around the world and well known to divers for their striking coloration and noisy feeding as they crunch on dead coral. Parrotfishes exhibit several types of complex mating systems that vary more by geographic location than by species (see Reproduction). They also have considerable ecological impacts on coral reefs through herbivory and bioerosion (see Ecosystem Roles).

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The parrotfishes are abundant around Caribbean coral reefs, especially in beds of seagrass or macroalgae. They are typically the predominant vertebrate herbivores on and off of the reef. The taxonomy of scarids in the region is relatively simple: there are four genera, but virtually all of the species belong to two large genera Scarus and Sparisoma. The two remaining species comprise the monotypic Cryptotomus roseus and Nicholsina usta, the latter with a sibling species in the eastern Pacific.

Larval scarids share most of their basic features with their labrid relatives, such as long and continuous dorsal and anal fins with slender spines, a relatively wide caudal peduncle, stub-like pelvic fins, a pointed snout and small terminal mouth, typically light markings and no spines on the head. They can be separated from larval labrids by having a row of melanophores along or beneath the base of the anal fin, typically extending into the caudal peduncle. A number of similar-appearing families share the anal-fin row of melanophores, but have many more dorsal and anal-fin elements, usually twice as many in larval labrisomids, chaenopsids, tripterygiids, and dactyloscopids. The latter group of larvae also have narrower caudal peduncles, larger mouths, long pelvic fins, and the anal-fin row of melanophores is right at the base of the fin rays and not deep as in the parrotfishes.

The parrotfish family is remarkably uniform in many aspects and all species share the invariant fin-ray count of D-IX,10 A-III,9. Given the morphological and meristic consistency of the family, especially within the two large genera, DNA-sequence analyses are required for identifications to the species level.

Pre-transitional scarid larvae can have eyes that are a narrowed vertical oval, often markedly so. This character is shared by larval razorfishes of Xyrichtys and some larval gobies. The eye becomes fully round in larval scarids just before the onset of transitional markings.

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Distribution

Parrotfishes are found primarily in tropical waters throughout the Atlantic, Indian, and Pacific oceans. However, some species inhabit subtropical waters, and some, such as Scarus ghobban, may venture far from reef environments.

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Physical Description

Morphology

Parrotfishes are characterized by their distinctive beak-like jaws, in which the teeth are fused together in most species, and a pharyngeal apparatus , which acts as a second set of jaws in the throat. In the pharyngeal apparatus, the teeth are arranged in rows and are highly specialized to grind, crop, and crush food as it is processed. Parrotfishes have large, cycloid scales , usually with 22-24 scales along the lateral line. The dorsal fin has nine spines and ten soft rays. The anal fin has three spines and nine soft rays, and the pelvic fins one spine and five soft rays. (Click here to see a fish diagram).

Some parrotfishes have a complex socio-sexual (socially influenced sexual change) system punctuated by three phases, and each phase change results in a different color pattern (See Reproduction: Mating Systems for a description of “phases” in parrotfishes). For instance, juveniles tend to have a drab mixture of browns, grays and blacks, but as they mature a distinct coloration emerges with the addition of red tones. A third set of colors is donned by males and by females that have recently undergone sex change into males. As these males mature, they exhibit bright, intricate patterns of reds, greens, and blues. This type of color change has been documented in Scarus, Sparisoma, Nicholsina, Bolbometapon, and Cryptotomus, but there are some monochromic (fishes that do not exhibit sexual color change) species that exhibit different types of sexual dimorphism.

Scarus coelestinus and Scarus coeruleus in the eastern Pacific and Scarus niger in the Indo-West Pacific exhibit no color differences. However, mature males of Scarus coelestinus and Scarus coeruleus develop more squared-off and prominent foreheads than smaller fish, while Scarus niger exhibits no physical differences other than size. Finally, fleshy tips on the upper and lower lobes of the caudal fin can be observed in mature males of Scarus rubroviolaceus, but are poorly developed on small males and females.

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Diagnostic Description

Description

Chiefly tropical. Distribution: Atlantic, Indian, and Pacific Oceans. Jaw teeth fused or parrotlike. Spines in dorsal fin 9; soft rays 10. Three spines in anal fin; soft rays 9. One spine in pelvic; soft rays 5. Caudal fin with 11 branched rays. Scales large; cycloid. Lateral line with usually 22-24 scales. Vertebrae 25. Herbivorous, usually scraping algae from dead coral substrates. At night, some species rest enveloped in their mucoid secretion. Sex change seems a common occurence, with the females either primary or secondary in most species. Many species could be identified by their live coloration but this may be lost in preservation, or can vary between juveniles and adults and with sex change.

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Ecology

Habitat

Most parrotfishes exclusively inhabit offshore coral reefs in tropical regions. However, a few species feed primarily on sea grasses and are most common in the Caribbean. Two other species, Nicholsina denticulate and Sparisoma cretense, are common over rocky reefs of the Gulf of California and Mediterranean Sea, respectively.

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Trophic Strategy

Parrotfishes are primarily herbivorous, grazing intensively on dead, algae-coated coral, vegetable material, and in some species sea grasses. Bump-headed parrotfishes, which consume significant amounts of live coral, are one exception. Key to the success of parrotfishes is their ability to take up plant material, detritus and calcareous sediment and process it through the action of the pharyngeal jaw. This chewing mechanism grinds ingested material into a fine paste and breaks down algal cells, releasing the cellular material for digestion. Like acanthurids, parrotfishes form large feeding groups, sometimes with multiple species, to overwhelm territorial fishes and deter predators.

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Associations

Parrotfishes have a major impact on coral reefs through intensive grazing and associated bioerosion. The grazing patterns of large schools of parrotfish have the effect of selecting for certain species of corals and algae, and preventing algae from choking out corals. Many parrotfishes feed on calcareous algae (algae that are high in mineral calcium) growing on dead, exposed coral by biting off chunks and turning them into a fine paste. This type of grazing contributes significantly to the process of bioerosion and the creation of sediment on reefs. For instance, it has been calculated that a single large parrotfish, Bolbometapon muricatum (bump-head parrotfish), consumes approximately one cubic meter of coral skeletons per year, and turns it into fine sediment. In this way large schools of bump-head parrotfish determine the fine-scale topography of coral reefs.

A separate ecological consequence of intense herbivory in parrotfishes is the conversion of plant material into fish flesh. The success of parrotfishes in consuming plant material unavailable to most other fishes and the large size of parrotfish populations makes them an important part of the predatory food chain.

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A unique feature of some parrotfishes is the production of a mucous envelope at night before resting. The envelope takes about 30 minutes to construct and is open at both ends to allow water flow. The secreted envelope is foul smelling and tasting, which may serve to deter nighttime predators that hunt by scent. Most parrotfishes seek out caves and ledges in the reef for protection at night, but parrotfishes in the genus Cryptotomus bury themselves in the sand like wrasses. After creating a hole in the sand Cryptotomus then produces its mucous nightgown.

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Life History and Behavior

Behavior

Most known forms of communication in parrotfishes are related to reproduction and are discussed in Reproduction: Mating Systems. However, in some species male coloration intensifies when defending its territory, which suggests that visual cues are used to deter invaders.

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Life Cycle

Tidal currents disperse parrotfish eggs, which begin to hatch approximately 25 hours after fertilization. Newly hatched larvae begin to feed after three days but the length of the planktonic stage is unknown. Most parrotfish species develop rapidly and reach maturity between two and four years.

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Life Expectancy

The maximum age of most parrotfishes is less than 20 years and most live less than five years. There is a general trend in the scarids for larger species to live longer. Subsequently, the largest scarid, Bolbometopon muricatum, is the one exception to the 20 year maximum age.

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Reproduction

Parrotfishes utilize some of the most complex and unusual reproduction systems known to fishes. Males can be either primary, i.e. born male, or secondary, i.e. females that have undergone sex change. In some species there are no secondary males while in others all individuals are born female (monandric) and change sex when necessary. In the most complex systems, species are diandric – both primary and secondary males exist in the population. In these species, individuals proceed through three distinct phases, marked by color differences. In fact, the color differences are so pronounced that for over 200 years researchers regarded some phases as distinct species. Sexually immature and drab colored juveniles represent the first phase. The second, known as the initial, phase (IP) can include sexually mature males or females, which are impossible to tell apart without internal examination or observation during spawning. The terminal phase (TP) includes only mature males, which display brilliant colors. TP males usually dominate reproductive activity through a harem-based social system. The death of a TP male serves as a social cue for an IP female to change sex and behavior. The morphology and behavior of IP males may also change in response to the death of a TP male. In some cases IP males attempt to infiltrate a TP male’s harem by masquerading as a female. In the so called “sneak spawning” attempt IP males follow spawning pairs into the water column and release a large cloud of gametes at peak spawning in an attempt to overwhelm fertilization by the TP male. IP males are well equipped to perform “sneak spawning” as they have larger testes and so are able to produce more gametes, while TP males have smaller testes and rely on aggression to deter other males.

The type of reproductive behavior described above and whether it involves paired, foraging group or mass spawning depends on a complex set of behavioral and geographic factors. For instance, some species, such as Scarus iseri, exhibit a wide range of reproductive behaviors depending on the area in which they are found. In Panama, Scarus iseri employs a system involving three classes of individuals: territorials, stationeries and foragers. Territorials are organized into groups that consist of a dominant female, several subordinate females and usually, but not always, a terminal (TP) male. Paired spawning occurs within the territory, which both males and females defend. Stationaries consistently use the same area for spawning but do not defend it, and foragers include groups of up to 500 individuals, mostly females. In Puerto Rico, initial phase (IP) and terminal phase (TP) individuals migrate to temporary spawning areas in deep water, usually in pairs. Finally, in Jamaica Scarus iseri emphasizes aspects of the foraging group system and spawning only takes place in groups. The three previous examples illustrate the flexibility of the socio-sexual mating systems found in parrotfishes. The reasons that different aspects of the basic spawning system manifest in different areas range from population density to competition for spawning sites and other resources to geographic factors like seasons and water temperature.

Mating System: polygynous ; polygynandrous (promiscuous)

In general, parrotfishes spawn year-round, usually at dusk. However, peak spawning occurs in summer for many species and there is evidence that some species have defined non-spawning periods. As discussed above, many species migrate to the outer edges of the reef to spawn but some spawn within defined territories. There is evidence that some scarids respond to the lunar cycle during spawning, but in others, spawning correlates closely with high tide, regardless of the time of the lunar month. In species that spawn several times during the day, the tidal cycle is followed closely since this is the optimal time for egg dispersal.

"The parrot fish feeds on algae and coral from coral reefs, and is one of the main causes of sand production from coral reefs. Its teeth are fused together to form a beak-like edge to the jaws for scraping at the coral, and it also has large flat-topped grinding teeth at the back of its throat for crushing the coral and algal mixture. The indigestible sand is excreted." (Foy and Oxford Scientific Films 1982:145)Learn more about this functional adaptation.

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In the Bahamas, the scales of some parrotfishes are used for decorating basketwork and shellflower arrangements, but the fish are not consumed. In other areas, parrotfishes are sometimes taken as food, but their flesh can be dangerous to humans as a result of accumulated ciguatera toxins.

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Wikipedia

Parrotfish

Parrotfishes are a group of about 90 species traditionally regarded as a family (Scaridae), but now often considered a subfamily (Scarinae) of the wrasses.[1] They are found in relatively shallow tropical and subtropical oceans throughout the world, displaying their largest species richness in the Indo-Pacific. They are found in coral reefs, rocky coasts, and seagrass beds, and play a significant role in bioerosion.[2][3][4]

Contents

Traditionally, the parrotfishes have been considered a family level taxon, Scaridae. Although phylogenetic and evolutionary analysis of parrotfishes is ongoing, they are now accepted to be a clade in the tribe Cheilini, and are now commonly referred to as scarine labrids (subfamily Scarinae, family Labridae).[1] Some authorities have preferred to maintain the parrotfishes as a family-level taxon,[5] resulting in Labridae not being monophyletic (unless split into several families).

Parrotfish are named for their dentition, which also is distinct from that of other labrids. Their numerous teeth are arranged in a tightly packed mosaic on the external surface of their jaw bones, forming a parrot-like beak with which they rasp algae from coral and other rocky substrates[6] (which contributes to the process of bioerosion).

Maximum sizes vary within the family, with the majority of species reaching 30–50 cm (12–20 in) in length. However, a few species reach lengths in excess of 1 m (3 ft 3 in), and the green humphead parrotfish can reach up to 1.3 m (4 ft 3 in).[7]

A number of parrotfish species, including the queen parrotfish (Scarus vetula), secrete a mucus cocoon, particularly at night.[8] Prior to going to sleep, some species extrude mucus from their mouths, forming a protective cocoon that envelops the fish, presumably hiding its scent from potential predators.[9][10] This mucus envelope may also act as an early warning system, allowing the parrotfish to flee when it detects predators such as moray eels disturbing the membrane.[10] The skin itself is covered in another mucous substance which may have antioxidant properties helpful in repairing bodily damage,[8][10] or repelling parasites, in addition to providing protection from UV light.[8]

Although they are considered to be herbivores, parrotfish eat a wide variety of reef organisms, and they are not necessarily vegetarian. Species such as the green humphead parrotfish (Bolbometopon muricatum) include coral (polyps) in their diets.[6] Their feeding activity is important for the production and distribution of coral sands in the reef biome, and can prevent algae from choking coral. The teeth grow continuously, replacing material worn away by feeding.[11] Their pharyngeal teeth grind up the coral and coralline algae[12] the fish ingest during feeding. After they digest the edible portions from the rock, they excrete it as sand, helping to create small islands and the sandy beaches of the Caribbean. One parrotfish can produce 90 kg (200 lb) of sand each year.[13] Or, very averagely (as there are so many variables i.e. size/species/location/depth etc), about 275 g per parrotfish per day. While feeding, parrotfish must be cognizant of predation by one of their main predators, the lemon shark. [14]

The bicolor parrotfish (Cetoscarus bicolor) was described by Rüppell in 1829. In 1835, he mistakenly described the terminal phase, featured on this photo, as a separate species, C. pulchellus

The development of parrotfish is complex and accompanied by a series of changes in color (polychromatism). Almost all species are sequential hermaphrodites, starting as females (known as the initial phase) and then changing to males (the terminal phase). However, in many species, for example the stoplight parrotfish (Sparisoma viride), a number of individuals develop directly to males (i.e., they do not start as females). These directly developing males usually most resemble the initial phase, and often display a different mating strategy than the terminal phase males of the same species.[15] A few species, for example the Mediterranean parrotfish (S. cretense), are secondary gonochorist, meaning some females do not change sex, and the ones that do, change from female to male while still immature (i.e., reproductively functioning females do not change to males).[16] The marbled parrotfish (Leptoscarus vaigiensis) is the only species of parrotfish known not to change sex.[11] In most species, the initial phase is dull red, brown, or grey, while the terminal phase is vividly green or blue with bright pink or yellow patches. The remarkably different terminal and initial phases were first described as separate species in several cases, but in some species, the phases are similar.

In most parrotfish species, juveniles have a different color pattern from adults. Juveniles of some tropical species can alter their color temporarily to mimic other species.[citation needed]

Parrotfish sleeping in a nook on a rock wall

Feeding parrotfish of most tropical species form large schools grouped by size. Harems of several females presided over by a single male are normal in most species, with the males vigorously defending their position from any challenge.

Parrotfish are pelagic spawners; they release many tiny, buoyant eggs into the water, which become part of the plankton. The eggs float freely, settling into the coral until hatching.

The sex change in parrot fish is accompanied by changes in circulating steroids. Females have high levels of estradiol, moderate levels of T and undetectable levels of the major fish androgen 11-ketotestosterone. During the transition from initial to terminal coloration phases, concentrations of 11-ketotestosterone rise dramatically and estrogen levels decline. If a female is injected with 11-ketotestosterone, it will cause a precocious change in gonadal, gametic and behavioral sex.

A commercial fishery exists for some of the larger tropical species, particularly in the Indo-Pacific. Protecting parrotfish is proposed as a way of saving Caribbean coral reefs from being overgrown with seaweed.[17] Despite their striking colors, their feeding behavior renders them highly unsuitable for most marine aquaria.[11]

A new study has discovered that the parrotfish is extremely important for the health of the Great Barrier Reef, it is the only one of thousands of reef fish species that regularly performs the task of scraping and cleaning inshore coral reefs. [18]